In the oil and gas exploration and production industry, well boreholes are drilled in order to access subsurface hydrocarbon-bearing formations. The drilled borehole may then be lined with sections of bore-lining tubing, known as casing or liner, which is then secured in place, typically using cement. A completion string may then be run into the borehole and operable to perform a number of different operations. For example, in some instances a formation may be susceptible to ingress of particulate matter, such as sand or the like, which if unabated can result in significant damage to equipment and tools and may also result in significantly decreased production from a particular formation zone. In order to combat the ingress of particulate matter, the completion string may be utilised to perform a gravel packing operation and/or to locate sand screens comprising filter media wrapped around a perforated base pipe and which permit the flow of fluid for extraction but prevent the passage of particulates.
More recently, “frac-pack” techniques have been developed which combines a hydraulic fracturing or “fracking” operation and a packing operation. The hydraulic fracturing operation involves the controlled injection of fluid into the formation to propagate fractures in the formation rock and increase flow of hydrocarbons for extraction while the packing operation involves the location of a packing material in the fractures and in the annulus between the completion string and the borehole wall for particulate control.
While frac-packing provides benefits in terms of increased production and reduced impact of particulate ingress, conventional frac-pack techniques and equipment still have a number of drawbacks. For example, completion strings are becoming ever more complex with the various completion string tools, handling areas, centralisers and couplings limiting the flow area available for production, reducing the utility of the formation. Moreover, in order to direct fluid into the formation when carrying out the fracturing operation the sand screens must be isolated so that the fluid being injected into the formation does not flow directly through them back into the completion string. This may be done by isolating the fluid return path at surface. By contrast, in order to avoid unpacked areas a return flow path is necessary during the packing operation so that the packing material—in the case of a frac-pack operation proppant—can be dehydrated from the residual carrier fluid and fill the annulus between the outside of the sand screens and the borehole. Also, during subsequent operations, such as hydrocarbon production or water injection, high rate fluid transfer through the sand screens is necessary so that the production or injection fluids can flow between the reservoir and the completion.